Conventional aluminum materials exhibit many desirable properties at ambient temperatures such as light weight and corrosion resistance. Moreover, they can be tailor-made for various applications with relative ease. Thus aluminum alloys have dominated the aircraft, missile, marine, transportation, packaging, and other industries.
Despite the well known advantages of conventional aluminum alloys, their physical properties can be degraded at high temperatures, for example above 250° C. Loss of strength is particularly noticeable, and this loss of strength is a major reason why aluminum alloys are generally absent in demanding high temperature applications. In place of aluminum, the art has been forced to rely on much more expensive alloys such as those containing titanium or tungsten as the main alloying metal.
Various attempts have been made to overcome the deficiencies of aluminum alloys at high temperatures. For example, U.S. Pat. No. 5,053,085 relates to “High strength, heat resistant aluminum based alloys” having at least one element from an M group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Ti, Mo, W, Ca, Li, Mg and Si and one element from X group consisting of Y, La Ce, Sm, Nd, Hf, Ta, and Mm (Misch metal) blended to various atomic percentage ratios. These various alloy combinations produce an amorphous, microcrystalline phase, or microcrystalline composite dispersions through rapid solidification of molten aluminum. Rapid solidification of the aluminum is accomplished through melt spinning techniques which produce ribbon or wire feed stock. The ribbon or wire feed stock can be crushed and consolidated into billets for fabrication into various products through conventional extrusion, forging, or rolling technologies.
Mechanical alloying is another attempt to produce high strength aluminum alloys. Nano particle strengthening of metal matrix materials is achieved in high-energy ball mills by reducing the particulates to fine dispersoids which strengthen the base alloy. A major problem associated with this technology is the uneven working of the particulates. A given volume of material is grossly over or under processed which leads to flaws in the final structure. U.S. Pat. No. 5,688,303 relates to a mechanical alloying process which incorporates the use of rolling mill technology to allegedly improve the homogenization of the mechanical alloying.
Some of the largest obstacles to mechanical alloying technology include lack of ductility and powder handling issues. Handling of the mechanically alloyed powders is dangerous since the protective oxide is removed from the aluminum powder which then becomes pyrophoric. Aluminum powder without the protective oxide will ignite instantaneously when exposed to atmosphere so extreme caution is required during the handling of the powder blend. Moreover, the use of high energy ball mills is very expensive and time consuming which results in higher material processing costs.
Other attempts to improve high temperature physical properties include the incorporation of additives. U.S. Pat. No. 6,287,714 relates to “Grain growth inhibitor for nanostructured materials”. Boron nitride (BN) is added as a grain growth inhibitor for nanostructure materials. This BN addition is added as an inorganic polymer at about 1% by weight and is uniformly dispersed at the grain boundaries which are decomposed during the heat treat temperature of the nanostructure material.
U.S. Pat. No. 6,398,843 relates to “Dispersion-strengthened aluminum alloy” for dispersion strengthened ceramic particle aluminum or aluminum alloys. This patent is based on blending ceramic particles (alumina, silicon carbide, titanium oxide, aluminum carbide, zirconium oxide, silicon nitride, or silicon dioxide) with a particle size <100 nm.
U.S. Pat. No. 6,630,008 relates to “Nanocrystalline metal matrix composites, and production methods” which involves using a chemical vapor deposition (CVD) process to fluidize aluminum powder which is coated with aluminum oxide, silicon carbide, or boron carbide then hot consolidated in the solid-state condition using heated sand as a pressure transmitting media.
U.S. Pat. No. 6,726,741 relates to aluminum composite material and manufacture based on an aluminum powder and a neutron absorber material, and a third particle. Mechanical alloying is used in the manufacturing process.
U.S. Pat. No. 6,852,275 relates to a process for production of inter-metallic compound-based composite materials. The technology is based on producing a metal powder preform and pressure infiltrating aluminum which results in a spontaneous combustion reaction to form inter-metallic compounds.
Rapid solidification processing (RSP) technology is another method employed to produce fine metallic powders. However, RSP has high costs associated with atomization of the high soluble alloying elements, powder production rates, chemistry control, and recovery steps needed in order to maintain the amorphous and nano size microstructures. The other major obstacle with RSP is the difficulty in fabrication of the materials.
These processes, while promising, have heretofore failed to address the long felt needs of manufacturing high temperature aluminum alloys on a commercial scale. Thus traditional, non-aluminum based alloys continue to dominate the high temperature alloy markets.